194 A. Pedler — Yolatility of some oftlie Gompoumh of Mercury. [No. 2, 



for, while in full sunshine mercary only is deposited by the action oi the 

 caustic soda on the mercuric chloride vapour, in tho dark mercm'ic oxide 

 is deposited, and the reaction appears to bo Hg Cl2+2NaH0 = HgO + 

 H304-2NaOl. 



So far as I have been able to ascertain the partial decomposition 

 and volatility of solid mercuric chloride at ordinary atmospheric tem- 

 peratures and under tho iniluence of sunlight have never previously been 

 noticed. J. Davy* apparently investigated thp properties of mercuric 

 chloride, and says the salt does not suifer decomposition when exposed 

 in the state of powder to sunshine. Tho salt is also well-known to be 

 volatile at high temperatures, for it melts at 265° and boils at 295°, but 

 beyond some vague statements that mercuric chloride is more volatile 

 than mercurous chloride, which is itself volatile only at about a red heat, 

 no precise statement is made that I can find, that this body is at all 

 volatile when in the solid state or at any temperature below its melting 

 point. 



Solutions of mercuric chloride are known to undergo slight change 

 when exposed to sunlight, and tho reaction is generally said to yield 

 mercurous chloride, oxygen, and hydrochloric acid,t or by others oxychlo- 

 ride and hydrochloric acid. In order to verify this point some experi- 

 ments were made by exposing such solutions to the rays of an Indian 

 sun. After exposure for about six months a solution of the morcurio 

 chloride gave a small quantity of a grey or greyish white precipitate, 

 and also some prismatic crystals of moderate size, which were colourless 

 and transparent. Both the crystals and the greyish white powder 

 were found to be mercurous chloride. No metallic mercui-y could bo 

 detected. The decomposition of the solution of mercuric chloride under 

 the influence of sunshine is therefore parallel to the decomposition of tho 

 salt in the solid state as above described. The decomposition of the 

 merc^^ric chloride is of course in both cases very incomplete. 



It has been proved by HannayJ in his paper on " new processes of 

 mercui-y estimation, &c.," tLat when a solution of mercuric chloride is 

 evaporated a portion of the salt is volatilized with the aqueous vapour, 

 and he made some quantitative experiments and showed, that in one case 

 over 5 per cent, of the salt could thus pass away. He also states 

 (p. 572) " that when solutions of mercuric chloride are evaporated or 

 boiled in a room even when well ventilated, the salt which is thus thrown 

 into the atmosphere is very injurious to the human system, in fact all 



* Gmeliu'8 Chemistry, Vol. 6, P. 53. 

 t Gmelin'B Chemistry, Vol. 6, P. 55. 

 j Journ. Chem. Boo. 1873, P. 565-575. 



